Retinitis pigmentosa represents a major, untreatable cause of visual loss in the United States. In early stages, the disease involves primarily rod-mediated vision as rod outer segments (ROS) become shortened and disorganized. The Naka-Rushton analysis of the full-field electroretinogram (ERG) will be used to evaluate diurnal variations in rod ERG parameters from light-entrained patients representing each major genetic type of retinitis pigmentosa and patients with cone-rod degeneration. The rate of recovery of ERG parameters following the diurnal light-triggered threshold increase will be used to determine whether ROS disc synthesis may be reduced or slowed in these patients. The diurnal variation in the rod ERG will also be used to evaluate regulatory mechanisms controlling photoreceptor renewal. Attempts will be made to alter the balance between disc shedding and disc synthesis in patients by manipulating the daily light cycles. Little is known about the natural course of rod loss in retinitis pigmentosa, despite the fact that night-blindness and elevated dark-adapted thresholds are typically the first symptoms associated with this disease. Rod ERGs, rod visual fields and rod pupillometry will be evaluated yearly in order to determine the rate and pattern of rod loss in patients with each genetic type of retinitis pigmentosa. Available evidence suggests that the rate of progression will be faster for rod-based function than that already established for cone-based function. The ability to assess therapeutic intervention in young patients with retinitis pigmentosa with measures that show rapid progression should enhance attempts to alter the natural history of this potentially blinding disease. Most cataracts occur in older patients who are also most likely to have age-related maculopathy. Focal electroretinographic measures of macular function will be obtained from patients before and after cataract surgery to determine the utility of this measure for detecting maculopathy in eyes with media opacities. Accurate detection of maculopathy is important so that both patient and clinician can make informed decisions concerning cataract surgery and anticipate post-surgical visual potential. Prospective studies of patients with unilateral macular holes will identify patients at risk for bilateral hole formation, help identify risk factors for macular hole formation, and lead to rational intervention to prevent macular hole formation in the fellow eye.